Pneumatic tube systems are well-known in the prior art. Pneumatic tube systems generally consist of a single tube which runs between two (2) stations. A carrier is transported between the stations by alternatively applying air pressure or suction to the end of the tube at one of the stations. Pneumatic tube systems are most often used in drive-in banking and toll collection systems. Examples of pneumatic tube systems are shown in U.S. Pat. Nos. 3,695,809; 3,599,898; 2,912,066; 4,135,684; and 4,189,261.
Most pneumatic tube systems employ a single blower or fan located at the first of the two stations. Such blowers typically have a single inlet or suction port and a single outlet or pressure port. The blowers are generally connected to one end of the tube through a series of valves. The other end of the tube which is at the second station of the system is open to atmosphere at all times.
When it is desired to transport the carrier from the first station where the blower is located to the second station of the system, the valves are operated so that the pressure port of the blower is connected to the tube behind the carrier and the inlet port of the blower is opened to atmosphere. This causes the air pressure to rise in the tube behind the carrier, pushing it toward the second station. The carrier is able to move because the air in the tube ahead of the carrier is able to exhaust at the second station. When it is desired to move the carrier from the second station back to the first station where the blower is located, the valves are repositioned so that the suction port of the blower is connected to the end of the tube at the first station and the pressure side of the blower is opened to atmosphere. The suction action on the carrier pulls it back to the first station. This is the basic operation of pneumatic tube systems. Suffice it to say that there are other elements which make up said systems such as mechanisms for loading and unloading carriers from the tube at the first and second stations.
The most costly and complex portions of a pneumatic tube system generally are the blower used to create the pressure and suction for moving the carrier and the valves used for alternatively applying pressure and suction to the tube. A typical blower and valve arrangement is shown in U.S. Pat. No. 2,912,066. This system employs four (4) valves positioned about a blower. These valves are actuated in pairs so as to either connect one port of the blower in an airtight manner to the tube while opening the other port of the blower to atmosphere. The system of this Patent is expensive to produce due to the cost of the four (4) valves, piping, and the electrical circuitry necessary to actuate the valves in the proper combinations. In addition, the blower of said system must be large to overcome the resistance to air flow created by the valves. The large number of cycles that the valves must make during operation of such a system increases the probability of valve failure. Another problem with systems of the type disclosed in this Patent is that the large blower, piping, and valves take up space at the station where they are located.
Later systems have attempted to reduce the cost associated with blower and valve arrangements for pneumatic tube systems by substituting the arrangement of four (4) valves with a single four-way valve. U.S. Pat. Nos. 4,135,684 and 3,659,809 disclose such arrangements. A single four-way valve, while less expensive than four (4) individual valves, is still a complex and expensive item. In addition, the flow resistance of a four-way valve, the tubing associated with such valve, and the potential for air leakage add to the size and power requirements of the blower which must be used in such systems.
Another type of blower and valve arrangement for a pneumatic tube system is shown in U.S. Pat. No. 4,189,261. This system is designed to reduce noise due to the rapid changes in air pressure which occur when pressure and suction are alternatively applied to a tube. In the arrangement shown in this Patent, the blower is placed in a divided enclosure so as to provide adjacent pressure and outlet ports. These ports are connected to an external air shifter valve which rotates between positions adjacent to the pressure and suction ports of the valve. The outlet of the air shifter valve is connected by a flexible tube to the end of the pneumatic tube. Thus by positioning the opening of the air shifter valve over one of the ports, suction or pressure is applied to the tube. While this system is less complex than systems which employ conventional four-way valves, certain deficiencies are apparent. The air shifter valve is complex and awkward as it requires considerable arcuate movement between positions over the two (2) ports. This may adversely affect its reliability. Also, there would likely be air leakage between the base plate and pivoting member of the valve. This air loss combined with the flow restriction associated with the valve and the flexible tubing to which it is connected would create losses requiring greater air flow and thus larger blower size. All of these factors add to the costs of such systems.
Thus there exists a need for a blower and valve apparatus for pneumatic tube systems which is less expensive to manufacture and operate, is more reliable, and is more energy efficient than those which are presently available.